1. Field of the Invention
The present invention relates to a plasma display panel (PDP), and more particularly, to a PDP having high discharge efficiency.
2. Description of the Related Art
For many years, television screens have been manufactured using cathode-ray-tube (CRT) technology. In a CRT television, an electron gun shoots a beam of electrons inside a glass tube. The electrons impact phosphor atoms at the screen (e.g., the wide end of the tube). In response, the excited phosphor atoms light up. Illuminating various areas of the phosphor coating with different colors at particular intensities produces the television image. Crisp images are the hallmark of CRT televisions, but such devices are bulky because a wide screen requires a correspondingly long electron gun in order for the electron stream to reach all parts of the screen.
A newer technology is the plasma display panel (PDP), which offers a wide screen that is relatively thin (e.g., approximately 6″). Put simply, a PDP forms an image by illuminating thousands of pixels, each made of a red, blue, and green fluorescent light. Like a CRT television, a PDP produces a full spectrum of colors by varying the illumination intensity of the different lights.
The central element in each fluorescent light is a plasma, e.g., a gas comprised of free-flowing ions and electrons. When an electric current is run through the plasma, free electrons collide with the gas atoms, causing them to release photons of energy. The gas atoms mostly used in PDP's emit ultraviolet photons that are invisible to the human eye, but which may be used to excite visible light photon, as explained below.
In a conventional PDP, xenon or neon gas is trapped in hundreds of thousands of tiny cells positioned between two plates of glass. Strips of electrodes are sandwiched between the glass plates, on both sides of the cells. Mounted above the cells are the transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer. Behind the cells, along the neon glass plate, are the address electrodes. Both the address electrodes and the display electrodes extend across the entire screen to form a grid. In the grid, the address electrodes are arranged in vertical columns and the display electrodes are arranged in horizontal rows. To ionize the gas in a particular cell, a computer associated with the PDP charges the electrodes that interact at that cell. It does this many times per second, charging each cell in turn.
When intersecting electrodes are charged (e.g., a voltage difference is created between them), electric current flows through the gas in the cell. This generates a fast flow of charged particles, which stimulates the gas atoms to release ultraviolet photons.
The inside walls of each cell are coated with a phosphor material (e.g., a material that absorbs the energy of an incident ultraviolet photon and emits a visible light photon). Thus, when impacted by the ultraviolet photons, the red, blue or green phosphor material emits red, blue or green light. Because every pixel is made up of a subpixel containing a red light phosphor, a subpixel containing a blue light phosphor and a subpixel containing a green light phosphor, the colors blend together to generate the overall color of the pixel.
By varying the pulses of current flowing through each cell, the PDP computer can decrease or increase the intensity of each subpixel color to create many combinations of red, green and blue. In this manner, a PDP can be made to produce different colors across the entire spectrum.
PDPs are categorized into alternating current (AC) PDPs and direct current (DC) PDPs. In a DC PDP, each electrode is directly exposed to the gas contained in a discharge cell, and voltage applied to each electrode is directly applied to the gas. In an AC PDP, respective electrodes are separated from the gas by a dielectric layer and do not absorb charged particles generated in discharge. Instead, the charged particles form wall charges, and the wall charges cause discharge.
Referring to FIG. 1 a conventional PDP includes first and second substrates 10 and 11 having inner surfaces facing each other. Address electrodes 12 and a dielectric layer 13 are sequentially formed above the second substrate 11. Barrier ribs 14 separating cells and preventing electric and optical cross talk between the pixels are formed on the dielectric layer 13. A fluorescent layer 15 is formed on the inner surface of each of the cells.
X electrodes X and Y electrodes Y are formed on the first substrate 10 such that the X electrodes X and the Y electrodes Y intersect the address electrodes 12 at right angles. Each of the X electrodes X includes a transparent electrode 16x and a bus electrode 17x, and each of the Y electrodes Y includes a transparent electrode 16y and a bus electrode 17y. The X electrodes X and the Y electrodes Y intersect the address electrodes 12 at respective cells.
A dielectric layer 18 covering the X electrodes X and Y electrodes Y is formed on the inner surface of the first substrate 10. A protection layer 19 composed of MgO is formed on the dielectric layer 18. A gas, such as xenon or neon, is injected into the cells interposed between the first and second substrates 10 and 11.
A voltage is applied to the address electrode 12, and to one of the X electrodes X, and the Y electrodes Y. Subsequently, an address discharge occurs between the electrodes. Discharged particles then migrate to the lower surface of the dielectric layer 18 of the first substrate 10. A sustain discharge occurs at the surface of the dielectric layer 18 by applying predetermined voltage between a X electrode X and a Y electrode Y of a particular cell. As a result, the gas contained in the cell is ionized to form a plasma, and a fluorescent substance coated on an inside surface of the cell is excited to produce a colored pixel.
Referring to FIG. 2, the sustain discharge occurs between the transparent electrodes 16x and 16y of the X electrodes X and the Y electrodes Y across a predetermined gap G1.
Optimally, initiation of the sustain discharge should occur in a wide area such that a discharge starting with the gap G1 is spread over an entire cell. However, when a conventional gap G1 is formed at predetermined intervals as shown in FIG. 2, initiation of the sustain discharge occurs locally, causing the spread of the discharge to be non-uniformly distributed. Consequently, a uniform field over the entire surface of the transparent electrodes 16x and 16y is not formed when the discharge is generated by applying a voltage to the X electrodes X and the Y electrodes Y, which are sustain discharge electrodes. Because a uniform field is not created, there is a portion of the transparent electrode that contributes little to the discharge. This unnecessary portion decreases the discharge efficiency of a discharge cell, and also decreases luminance by covering (e.g., blocking) an area of the discharge cell.
A solution is needed that increases the discharge efficiency of each cell by ensuring a more uniform distribution of the sustain discharge.